1. Field of the Invention
The invention concerns a method of manufacturing optical waveguides based on polymer materials.
2. Description of the Prior Art
Optical fibers are used not only to transmit data but also to process data in a very broad meaning of the term. Modulation, switching, multiplexing, repolarization, etc functions can therefore be implemented by associating an optical waveguide with integrated optical circuits.
Lateral confinement optical waveguides are conventionally implemented on the surface of monocrystalline lithium niobate by doping the crystal, usually with thermally diffused titanium. The refractive index of the doped region is increased so that this region can guide light in a certain range of wavelengths.
The guide structures previously used are mainly structures of the following types:
"photobleaching" structures based on lowering the refractive index of the active polymer after exposure to ultraviolet light;
"SPP" structures in which a metal strip is deposited onto the active layer; the active molecules in the material are oriented by applying an electric field between this strip and the substrate; the extraordinary index is increased under the metal strip whereas the ordinary index is reduced by the Pockels effect; the part of the active layer under the metal strip therefore becomes an optical waveguide for a TM wave (polarized in the plane of the layer);
"channel waveguide" structures in which the light is confined in the active polymer above the recessed part of the buffer layer by varying the effective index in this area.
The structures described above all have the same drawback: lateral confinement is poor because it is due to the relatively small refractive index difference (in the order of 5.times.10.sup.-3). The present invention concerns a new technique for fabricating optical waveguides producing very large refractive index differences to either side of the active strip guide and improving lateral confinement by reducing light losses; the refractive index difference (0.01&lt;.DELTA.n&lt;0.4) varies with the materials employed. The lateral confinement property is crucial in the case of more complex components. In components such as electro-optic X junctions, in which the waveguides intersect at angles in the order of 1.degree., poor confinement of the light wave causes light to be lost from one waveguide to the other, producing crosstalk between channels.